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Electrical power can be transmitted by
Overhead system
Underground system
Either (a) or (b)
None of above
Either (a) or (b)
Electrical power is transmitted from generating stations to load centers using either overhead transmission lines or underground cables. Overhead systems use bare conductors supported by insulators on towers, whereas underground systems utilize insulated cables buried in trenches or ducts.
Electrical power is transmitted from generating stations to load centers using either overhead transmission lines or underground cables. Overhead systems use bare conductors supported by insulators on towers, whereas underground systems utilize insulated cables buried in trenches or ducts.
VdropтАЛ=I├ЧR тАФ Voltage drop calculation in transmission lines
P=3тАЛ├ЧVLтАЛ├ЧILтАЛ├Чcos╧Х тАФ Real power transmitted in a 3-phase system
The choice between overhead and underground systems depends on factors like voltage level, cost, environmental conditions, and maintenance requirements. Overhead lines rely on the air gap as the primary insulation, making them more economical for long-distance high-voltage transmission. Underground cables use solid or oil-impregnated dielectric materials for insulation, which is safer and more reliable in congested urban areas despite significantly higher costs.
Overhead systems are preferred for long-distance, high-voltage EHV/UHV transmission due to lower cost.
Underground systems are primarily used in densely populated urban areas, industrial plants, and subsea crossings.
The surge impedance loading is a critical factor in designing transmission line length.
Underground cables have high charging currents due to high shunt capacitance compared to overhead lines.
Overhead: Lower initial cost, easy fault location, simple repairs.
Underground: Aesthetics, immunity to atmospheric hazards (lightning/storms), low maintenance.
Overhead: Vulnerable to weather, high maintenance, interference with communication lines.
Underground: Very high installation cost, difficult fault localization, thermal limits on current carrying capacity.
Overhead: Rural electrification, Long-distance bulk power transfer.
Underground: City distribution, substation connectivity, airports, high-security facilities.
| Feature | Overhead | Underground |
|---|---|---|
Initial Cost | Low | High |
Fault Detection | Easy | Difficult |
Transmission lines are typically defined as systems operating at voltages above 33 kV.
Option D is incorrect because power transmission is exclusively achieved through these two physical mediums in current power systems.
C is correct тАФ Electrical power is reliably transmitted using either overhead lines or underground cables, depending on the specific economic and technical constraints of the project.
Always remember that underground cables have higher shunt capacitance C than overhead lines, leading to higher charging current, which can limit the maximum transmission length.